Hmm, hard one as you are not travelling a full week and commuter tickets tend to be geared to those that are. You are also outside the Leap card zone so you can't look into that (just yet anyway!)
A couple of thoughts.
Irishrail is likely to be an expensive option, the weekly,monthly and even probably the annual ticket will not present a saving to you on buying a daily ticket.
JJ do a weekly ticket for £30 from Naas, but again this may not prove good value for three days.
Have you asked if your employer does the taxsaver scheme? If they do, you can avail of it for Irish Rail, Bus Éireann and JJ Kavanagh's for monthly and annual commuter tickets, this would make them substantially better value.